Mortal Kombat II/Game Gear
The Sega Game Gear was essentially the same hardware as the Sega Master System. Their versions of MK2 are logically quite similar. The screen sizes are cropped differently to account for different resolutions. The sound is virtually identical. The Game Gear gets the nudge over the Master System because it looks so much brighter and plays a tad better (due to having an extra button to work with).
It takes a while to learn how to execute moves with only two attack buttons (i.e. D+kick for a leg sweep). The start button serves as block but on an actual Game Gear is awkward to use.
The characters look fairly good, they're bright and colorful. Plus they're almost the same relative height as the arcade version. On the downside, the backgrounds are cropped along the top.
The soundtrack is pretty scratchy and experiences some brief pauses at times. Extras:
Three levels of difficultly to choose from.